Rubber-backed propeller



Y 5, 1953 s. G. BART 2,637,404

oz/WW Patented May 5, .1953

UNITED STATES PATENT OFFICE Claims. Cl. 170-459;)

1 The invention relates in generalto amultilayered, sandwich material of the type in which a layer of metal is deposited-electrolytica1ly on .a

layer of rubber for use wherever such multilayered materials are suitable, and specifically "relates to a rubber-backed aeroplane propeller 'blade and similar constitutes a division of my pending application entitled, Rubber Bonding Process, Serial No. 183,595, filed September 7, 1950.

aerofoils. This application The primary object of the invention is-to provide an improved form-of aerof-oil in which the 'outer'shell-forming surface of the electrolytically deposited covering will remain permanently bonded to the underlying rubber or at least bonded for a much longer period than has been possible prior to theproduction ofarticles manufactured by the method disclosed in-the aboveidentified parent application.

' Among the other objects of the invention is to produce an aeroplane propeller "blade which will be light in weight, whose outer surface will meet aerodynamic requirement of'a smooth, continuous, uninterrupted outer ,metallic skin, and to provide a cushioning effect to the outer skin and to form the propeller as'an integral one-piece article.

It has been known-to form theouter, air-fbeating surfaces of propellers at least in part of sheet steel laid on woodand of chromium plating on steel, but it is difiicult'to shape the steel exactly to the aerodynamic configuration now demanded of propeller blade designs and under severe operating conditions chromium'plating on steel has a tendencyto develop minute cracks and eventuallydisintegrates in service.

Depositing nickel electrolytically, especially when deposited on rubber as herein featured, provides a one-piece outer layer orskin to the propeller blade which does not need .to hemeformed as in the case of the, steeliacings and -does notgcrack orohip as 'does'the chromium and, on thecontrary providesi a smooth. hardsur'face, particularly at its leading ed e, and wherever else there is required'a surface highly resistantjto the abrading 'and erosive-"eiiectof water, sand and other solids often presentin the air.

While aeroplane propellers are usually considered to be rigidbodies actually they; are "preferably required to have some small degree of flexibility in certain partsand-relative-rigidity in otherparts. 'For instance; the leading andtrailingedges,-as-well as thetips, are usuallyrequired to be rigid, more .or lesspwhile parts' therebetween forming the cambre surfaces should possess at least'a slight degree of fiexure. Also, in aeroplane propeller blades andsimilar aerofoilsthere greater wear, especially at the leading edge and tip. and, accordingly, the present disclosure features a peculiar apportioning or" the electro-metal which forms the outer skin to provide for-relatively thick cross section of material and for greater density of material and thus for a greater hardness of material at the leading and-trailing edges and at the tips, and a relatively thin and more flexible cross section of material in that .partof the skin which forms the cambre portions of the blade.

'Briefly, this is attained by-using astress-"free nickel and by building up and thus thickening the nickel deposited on the narrow edges forming the leading and trailing edges and on the con- .vergingsurfaces outlining thetips of the blade.

Various objects of the invention will be obvious from a consideration of the accompanying drawings in which:

'Figvlis a view in planof an aeroplane propeller blade of conventional design forming a preierred embodiment of the invention, a portion of the outer metal shell being removed to show the underlying rubber-containing layer and a portion of the metaltip is shown in section inthe plane of the blade;

Fig. 2 is a transverse sectional view takenon the line 2-2 of-Fig. l,somewhat enlarged, with -the-mid-portion broken away to save space and with the layers shown approximately in their relative dimensions and Fig. 3 isa very much enlarged sectional showing on-a scaleof-about 1 to 5000 of the several layers of material including the two initial layers of rubber which eventually become the single layer of rubber, inthe blocked-off portion outlined by dotted lines at the upper centralportion of the'iinished-blade, as shown in Fig. 2.

The finishedblade H] as shown inFigjlis. of conventional design and as shown in Fig. ,2 ,includes an inner core l iormingthe base on which a rubber backing layer 12 is formed as herein featured, "and on which rubber layer anouter layer or shell [3 of electrolytically deposited nickel isformed. "The blade when completely formed is-provided with a'relatively thick leading edge I' l rounding in-a vertical plane as shown in Fig. Zen arelatively large radius anda-relatively thin trailing-edge! 5 similarly rounding on a relatively small radius. Between the leading and trailing edges the blade provides an. upper camber -forining surface [Band a lower camberforming surface l1 merging at their ends into a tip l8 as is usual in propeller blades. The inner core or base I l in this case is preformed of forged or cast aluminum and of such size and contour so that when the different layers are added thereto as hereinafter described there will be produced the finished blade with its desired size, configuration and structural strength to respond to approved aerodynamic requirements of such blades. While forged aluminum has been selected because of its light weight, cheapness and other desirable properties, it is suggested that the core may be made of other metals, or may even be made of wood or plastics.

In practicing the method herein featured it is necessary that the exposed surface of the aluminum core must be cleared of all adhering grease and other foreign matter. To obtain the necessary cleanliness it is suggested that the core surface be anodized as by treating it in an acid bath of an electrolytic cell with the current reversed.

A thin layer of plastic bonding material iii, of which several suitable types are on the market and most of them containing a pheno1-form aldehyde base, is applied to the cleaned surface of the aluminum core. Such a. bonding product manufactured for this purpose by U. S. Stoneware Co., of Tallmadge, Ohio, under the tradename Reonite, has been used with success. The bonding material is applied in several coats and permitted to dry between succeeding coats. The core so coated is baked with infrared heat in an oven for about one hour and at a temperature of about 150 degrees F., and then removed from the oven. This plastic layer l9 provided ,a protective coating to the aluminum and adheres well to the same.

Three or four coats of chlorinated or bonding rubber cement free of sulphur and with a suitable solvent are then sprayed onto the plastic bonding material so baked on the core with about fifteen minutes of air drying between the appli cation of each coat to remove the solvent and to leave a thin, rubber-containing, base-coating bonding layer 20 of chlorinated rubber, in the illustrated case having a thickness of about 0.0005 of an inch.

Seven to twenty coats of neoprene (polychloroprene) rubber cement which does not require any sulphur for curing are then sprayed on the bonding layer 20 with air drying between succeeding coats to form a relatively thick cushioning neoprene rubber cement layer 2|, in the i1- lustrated case having a thickness of about 0.004 of an inch. Neoprene rubber cement as it appears on the market contains, in addition to its rubber content, carbon black, zinc oxide, magnesia and certain other ingredients in small proportions.

In those cases where the neoprene rubber cement or equivalent cushion-forming, rubberlike material will adhere to whatever material may be used to form the core H, the bonding layer 20 may be omitted.

This neoprene rubber cement so used contains an accelerator such as magnesium oxide (MgO- magnesia-which is present in about two per cent and is operative to facilitate the aging of the rubber and to toughen the neoprene to a rubber-like mass within the relatively short period of heating time employed in practicing the curing steps herein featured. The two layers of rubber thus eventually forming the all-rubber backing layer 12 are then given a preliminary, that is, an incomplete or partial curing by baking the core so rubber-coated in an oven 4 for about two and one-half hours at a temperature of about 150 degrees F. On removal from the oven and thus while the rubber is hot and tacky, at least, on its exposed surface, a layer 22 of graphite is dusted onto the surface of the rubber to form a continuous layer of a cathodeforming material. While graphite is suggested, other cathode-forming conductive materials such as powdered metal may be used.

It is suggested that, in place of dusting the graphite onto the surface to form the layer 22, the graphite be added to the last coat of the sprayed layer 2! mixed into the same preferably in amounts of two to ten percent of graphite to the rubber in this last coating. This, of course, eliminates layer 22 as a distinctive all-graphite layer.

The rubber-coated core so dusted with raphite or faced with a thin graphite-containing film is positioned within the electrolyte of an electrolytic cell containing nickel and the cell caused to function conventionally so that eventually the rubber-coated core II is enclosed in a onepiece, continuous skin or shell l3 of electrolytic nickel deposited by means of a current of high depositing density and otherwise following conventional practices in this respect. In order that the deposited nickel layer be free of stress and form the same as bright nickel, an additional agent such as saccharine is added to the electrolyte of the Watts type to make of it a modined Watts solution. While nickel is suggested as thc, preferred metal to form the outer shell I3, it is suggested that the shell may be formed of two electro-metals, for instance, an inner layer of copper and an outer layer of nickel, or it may be formed of a metal harder than nickel, such as tungsten, titanium, molybdenum, or alloys which can be plated. It is suggested that the outer shell 13 be electroformed iron with a chromium plate.

It is a distinctive feature of this disclosure that the electrolytic bath be maintained at a. temperature ranging between degrees and ,165 degrees F., preferably nearer than 125 degrees F2, for ten to twenty hours while depositing its nickel. This final heat treatment in the bath has the effect of completing the curing of the neoprene rubber cement and apparently effects a curing of the chlorinated rubber, for the entire layer !2 appears to have its strength improved by the curing process herein featured. During the metal-depositing step the bath is heated as by means of steam pipes and care is exercised to keep the bath not materially greater than 150 degrees F., for a temperature materially greater than 150 degrees F. tends to destroy the adhesive qualities of the rubber and if more than 150 degrees F. is used the time the rubber is exposed to such temperature should be quite brief.

The resulting, completely cured rubber layer I 2 thus formed by the amalgamation of the rubbercontaining layers l9 and 20 forms a tough, resilient rubber bond with an improved adhesion to both the aluminum core and the resulting outer nickel shell over anything which has been found heretofore. Neoprene rubber cement does not adhere well to the plastic layer l9 and this is the reason for using the chlorinated layer 20 therebetween. As the plastic bonding material l9 adheres to the basic aluminum core H, as the first layer of chlorinated rubber adheres to the bonding material I 9, as each layer of rubber is bonded to the next preceding layer, and as the final electro-metal is bonded to the neoprene rubber cement it follows that each superposed layer is estate;

bonded to the layer next beneath it and thus the rubber completely fills the spatetetweeri the innet core and the outer shell and there re rained, in effect, a one-piece laminated sandwich material. Over an extensive period of use even under conditions where there was much vibration of the resulting product, for instance, in the propeller, the nickel covering adhered tena'eioiisly to the rubber and no blisters or raised spots formed.

The nickel skin covering I3 rormedas herein featured in forming the propeller neither homogeneous nor of equal cross section of material in its several parts, By reason oi the narrowed edges provided by the sharply rounded leading edge l4 and the even more sharply rounded trailing edge l5 there will be a tendency of the bath in its normal operation to form a denser deposit of nickel on the narrow edges than on the more fiat camber-forming surfaces (6 and I1. Also, by arranging a selective deposition of the anodes in the bath relative to the cathode surfaces and following known controls in this respect, there is presented first by the graphite-coated surface, and subsequently by the successive deposits of the nickel and, if necessary by the use of selective masking processes, a deposition of the nickel which can be regulated to obtain a relatively thin cross section of material at the camberforming surfaces and a very much increased cross section of material in those parts which form the leading and trailing edges and the tip.

In one embodiment of the invention the nickel skin [3 of the camber-forming parts l6 and I! was formed to a depth of about eight to tenthousandths of an inch. Despite the fact that the skin is formed of nickel, its extreme thinness tends to give a certain degree of ductility and flexibility to the blade considered as a whole, and particularly in its mid-width portion, which thus provides a hinge effect along the longitudinal medial plane of the blade midway between the leading and trailing edges. On the contrary, the body of nickel which forms the leading edge I4 is quite thick, massive, rigid and harder than the body of nickel which defines the upper and lower camber-forming parts. The body forming the shell l3 has a thickness in the line of thrust of the propeller blade of from ten to eighty-thousandths of an inch, depending on the use to which the propeller blade is to be put, and in any case merging from its thick leading edge with progressive reduction in thickness smoothly into the camber-forming parts at top and bottom of the blade. A maximum thickness of nickel at the leading edge of about forty-thousandths of an inch is found to be ideal for propellers and for similar forms of aeroioils.

While the abrasive wear on the trailing edge is not as great as on the leading edge of propellers, it is suggested that the nickel in the part which forms the trailing edge likewise be made thicker, more rigid, denser and thus harder along the line of thrust than in the camber-forming parts, and likewise merge with gradually reduced cross section of metal into the thin, camber-forming parts. In the illustrated case the maximum thickness of nickel at the trailing edge is slightly less than is the thickess of metal in the leading edge.

In general, the propeller blade presents an external, continuous, air-engaging surface formed of a skin of tough, strain-free nickel free of projections of any kind and which skin as it is deposited electrolytically can be made to give an air-beating surface which can be formed accurately to the minute dimensions of aerodynamic of propeller blades.

1. An aeroplane propeller blade comprising a preformed relatively rigid core provided with a leading edge, a trailing edge and with upper and lower camber surfaces therebetween, said core at a mid-length portion thereof encircled by two superposed layers of material, that is, an inner layer of a rubber-like material and a thin outer layer of metal, said rubber-like material functioning as a resilient bond between the preformed rigid core and the thin outer layer of metal, the thickness of the rubber-like material being of the order of four thousandths of an inch and substantially uniform in cross section, the thickness of the layer of metal gradually and progressively increasing from about eight to ten-thousandths of an inch in the camber-forming portions to about forty-thousandths of an inch in the edgeforming portions and said layer of metal presenting a continuous unbroken and smooth surface in its air-beating portions.

2. A substantially rigid aeroplane propeller blade having a slight degree of flexibility along its longitudinal medial plane, said blade including an inner, preformed, relatively rigid core functioning to give configuration and strength to the blade, an intermediate layer of a rubberlike cushioning material enclosing the core and an outer skin of strain-free metal enclosing the layer of cushioning material, presenting a continuous unbroken surface to the air-beating Portions of the blade and defining the leading edge, the trailing edge and the tip of the blade and between the leading and trailing edges forming the upper and lower camber portions of the blade, said outer metal skin being of relatively thin cross section of material in its camber-forming portion to provide for flexibility and thus to provide for a hinge efiect along the medial plane of the blade, and said metal skin in the parts forming the leading and trailing edges and the tip having a cross section of material greater than the portions which form the camber portions, thus providing more rigidity in th edges and tip than in the camber portions, thereby to provide a relatively thin and more flexible cross section of material in that portion of the skin which forms the camber portions of the blade than in the edge and tip forming portions.

3. The blade defined in claim 2 and in which the portion of the metal skin forming one of the edges has a greater density and a greater hardness of metal than the metal skin which forms the camber portions of the blade.

4. A substantially rigid aeroplane propeller blade including an inner preformed metallic core functioning to give configuration and strength to the blade as a whole, an intermediate layer of a cushioning material enclosing the core and an outer skin of electro-metal enclosing the layer of cushioning material, a thin layer of a plastic bonding material between the cushioning layer References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,248,151 Mott Nov. 27, 1917 1,329,735 Wicker Feb. 3, 1920 1,662,430 Maas Mar. 13, 1928 "Aviation Operations February 1950, pp. 31 I 15 and 62 (copy in Div. 22).

8 Name -Date:;' Damerell Feb. 11, 1941 Caldwell Mar. 10, 1942 Saunders May 22, 1945 Larsen May 21, 1946 Garvey Mar. 25, 1947 Martin Jan. 17, 1950 McCulloch Apr. 25, 1950 Bradley July 4, 1950 Scholl May -1, 1951 Kuhn Jan. 8, 1952 OTHER REFERENCES 

